(a) Field of the Invention
The present invention concerns an oxynitride film containing gallium and/or aluminum, and its manufacturing method.
Such oxynitride film as stated above is very useful and effective for use not only as an optical but also an electrical material because it is possible to continuously vary the values of, for example, refractive index and dielectric constant of this film by varying the proportion between oxygen and nitrogen which are contained in the film to be formed. Furthermore, by depositing such oxynitride film on a semiconductor surface, it is possible to use it as a surface passivation film thereof also. Here, the term "surface passivation film" means not only a surface-protection film in its narrow sense, but also a gate-insulating film of such articles as insulated-gate type field effect transistor, insulated-gate type static induction transistor, and insulated-gate type semiconductor integrated circuit using these transistors, and furthermore the film may serve as: a selective diffusion film employed in the planar semiconductor device manufacturing technique, a thin encapsulating film in post-ion-implantation annealing technique, a masking film employed in the selective growth technique, and a thin insulating film which is incorporated in those active portions of an active device and an insulating film for passive use other than the use mentioned above.
(b) Description of the Prior Art
Description will hereunder be made firstly with respect to surface passivation of III-V compound semiconductors. Known surface passivation methods for III-V compound semiconductors which are made typically of GaAs may be divided roughly into the following three types.
(1) A method of using, also for III-V semiconductors, such deposited films as SiO.sub.2, Si.sub.3 N.sub.4, Al.sub.2 O.sub.3 and P.sub.2 O.sub.5 which have been used as passivation films for the surfaces of silicon semiconductors. This known method, while having the drawback that the deposition temperature is relatively high, is being used quite frequently at present. Especially an SiO.sub.2 film is widely used in technical fields excluding those semiconductor devices which are designed to use their surface portions just beneath the interface with the SiO.sub.2 as an active region, for reasons such as easiness of formation of this film and also in view of the utilization of the accumulated knowledges concerning the method of producing planar type silicon semiconductor devices, and for like reasons, in spite of the important drawbacks that this SiO.sub.2 film tends to take in Ga from the surface of a substrate made of GaAs or GaP and that thereby it will damage the stoichiometry of the surface of the substrate.
(2) A method of forming, on a substrate, a native oxide film corresponding to a thermal oxidation film of silicon, in place of the deposited film stated in (1) above. Among those techniques belonging to the type categorized by this paragraph (2), the anodic oxidation method has the advantage that an insulating thin film can be formed at a markedly low temperature as compared with the deposition method and also with the thermal oxidation method, irrespective of the instances wherein a solution is used or a gas plasma is used. Conversely, however, this anodic oxidation method has the disadvantage that it is thermally unstable, and therefore, it has the drawback that the quality of the film will change substantially at a temperature below the temperature range adopted for thermal diffusion of impurities and post-ion-implantation annealing. Furthermore, the interface between an anodic oxide film and a substrate made of GaAs or GaP tends to contain a number of defects, so that when this film is utilized as an insulating film of IG-FET (Insulated-Gate Type FET), there still cannot be obtained as yet a large value of surface mobility comparable with that within the bulk, and thus at the current technical stage, it is not possible for the anodic oxide film to fully display those advantages and features on applying it to the surface of GaAs and GaP substrates which are represented by higher mobility as compared with a silicon substrate. In III-V semiconductors which, essentially, are binary compounds, a direct thermal oxidation of their surfaces has not yet produced any satisfactory results with respect to the quality of the film produced or to the state of interface. Such native oxide film has the further drawback that it is dissolved in acids such as HF, HCl, and H.sub.2 SO.sub.4. Therefore, native oxide films inconveniently cannot be used in such manufacturing process as would comprise a number of steps.
(3) A method of performing chemical oxidation by the use of, for example, hot hydrogen peroxide solution. This method is entailed by limitation in the thickness of oxide film which is formed, and accordingly the extent of application of this method is limited also.
As discussed above, these known surface passivation methods for III-V compound semiconductors invariably have both strong points and weak points.